Mobile communication systems were developed to provide the subscribers with voice communication services on the move. Recently, the mobile communication systems have evolved to the level of supporting high speed data communication services beyond the early voice-oriented services. However, the resource shortage and user requirements for higher speed services spur the evolution to more advanced mobile communication systems. Recently, standardization for a Long Term Evolution (LTE)/LTE-Advanced (LTE-A) system, as one of the next-generation mobile communication systems, is underway in the 3rd Generation Partnership Project (3GPP). LTE is a technology designed to provide high speed packet-based communication of up to 100 Mbps. With the diversification of the types of services using wireless mobile communication system, there is a need of a new technology for supporting the newly introduced service more efficiently and, as a consequence, research and the development of new methods and technologies are being conducted for use in the wireless mobile communication system.
The Device to Device (D2D) communication is a technology being researched to make it possible for a terminal to communicate with neighboring terminals directly. The D2D communication technology makes it possible for a UE to discover other UEs located nearby and communicated with another UE directly if necessary. With the D2D communication technology, the terminal can discover neighboring terminals (hereinafter, referred to as D2D-D) and perform Direct Communication with a target terminal (hereinafter, referred to as D2D-C). The D2D communication is advantageous in terms of radio resource efficiency in comparison to the legacy radio network-assisted communication via a base station. Since the D2D communication support a neighboring terminal discovery function in which the terminal is capable of sending necessary information to a target terminal directly, it is possible to support the new services such as Social Networking Service (SNS) and advertisement service efficiently.